The electromotive force (EMF) is the maximum potential difference between two electrodes of a galvanic or voltaic cell, where the standard hydrogen electrode is on the left-hand side for the following cell:
12Pt ElectrodeH2Aqueous Electrolyte10−3 M Fe(ClO4)3PtSolution10−3 M Fe(ClO4)2The EMF is called the electrode potential of the electrode placed on the right-hand side in the graphical scheme of the cell, but only when the liquid junction between the solutions can be neglected or calculated, or if it does not exist at all.
The electrode potential of the electrode on the right-hand side (often called the oxidation-reduction potential) is given by the Nernst equationEFe3+/Fe2+=EFe3+/Fe2+0+(RT/F)ln(aFe3+/aFe2+)This relationship follows from equation (2.21) when (μFe3−0−μFe2+0)/F is set equal to EFe3+/Fe2+0 and the pH and ln pH2 are equal to zero. In the subscript of the symbol for the electrode potential the symbols for the oxidized and reduced components of the oxidation-reduction system are indicated. With more complex reactions it is particularly recommended to write the whole reaction that takes place in the right-hand half of the cell after symbol E (the ‘half-cell’ reaction); thus, in the present caseEFe3+/Fe2+≡E(Fe3++e=Fe2+)
Quantity EFe3+/Fe2+0 is termed the standard electrode potential. It characterizes the oxidizing or reducing ability of the component of oxidation-reduction systems. With more positive standard electrode potentials, the oxidized form of the system is a stronger oxidant and the reduced form is a weaker reductant. Similarly, with a more negative standard potential, the reduced component of the oxidation-reduction system is a stronger reductant and the oxidized form a weaker oxidant.
The standard electrode E0, in its standard usage in the Nernst equation, equation (1-2) is described as:
  E  =            E      0        +                            2.3          ⁢                                          ⁢          RT                nF            ⁢      log      ⁢                                    C            0                    ⁡                      (                          0              ,              t                        )                                                C            R                    ⁡                      (                          0              ,              t                        )                              Where E0 is the standard potential for the redox reaction, R is the universal gas constant (8.314 JK−1mol−1), T is the Kelvin temperature, n is the number of electrons transferred in the reaction, and F is the Faraday constant (96,487 coulombs). On the negative side of E0, the oxidized form thus tends to be reduced, and the forward reaction (i.e., reduction) is more favorable. The current resulting from a change in oxidation state of the electroactive species is termed the faradaic
Previous work describes using conversion of functional groups attached to a transitional metal complex resulting in quantifiable electrochemical signal at two unique potentials, Eo1 and Eo2. See for example, U.S. Pat. No. 11-1005-US11-1005-US2, all herein incorporated by reference in their entirety. The methods generally comprise binding an analyte within a sandwich of binding ligands which may have a functional tag, on a solid support other than the electrode. After target binding, a peroxide generating moiety or an intermediary enzyme and substrate are added, which generates hydrogen peroxide. The redox active complex is bound to an electrode and comprises a peroxide sensitive moiety (PSM). The peroxide generated from the enzyme system reacts with the PSM, removing a self-immolative moiety (SIM) and converting functional groups attached to a transitional metal complex resulting in quantifiable electrochemical signal at two unique potentials, Eo1 and Eo2.
Patients afflicted with diabetes are incapable of metabolizing glucose in a conventional manner resulting in a build-up of glucose in their blood and urine. Conventionally, the glucose level in such body fluids is taken as a measure of the state of the diabetic condition which, in turn, is used as a guide for the amount of insulin or other agent to be taken or of the need to change the patient's diet. This works moderately well except that the glucose level may fluctuate widely in dependence upon the time and content of the last meal, the last insulin injection, and the like. Thus, the reading will reflect an instantaneous condition which might not truly identify the longer term state of the diabetic condition. To circumvent the single glucose determination, more elaborate measurements (e.g., the 4 to 8 hour glucose tolerance tests) are used to measure the blood levels of glucose following an oral administration. These latter tests are time consuming, expensive and the individual must fast during the course of the assay. It is known that another effect of the diabetic condition is an increase in the amount of glycated hemoglobin (Hb) in the blood of the diabetic. The glycation of hemoglobin occurs by a non-enzymatic reaction involving glucose and the alpha-amino group of valine. The glycation reaction is governed by the concentration of the reactants, e.g., hemoglobin and glucose. In a normal (non-diabetic) individual approximately 3% of the total hemoglobin is glycated. Hemoglobin tetramers with a 1-deoxyfructo-valine on the N-terminus of a beta-chain are identified as being glycated or A1c hemoglobin. With hemoglobin, the A1c level is raised 5 to 12%. Since the circulating life span of hemoglobin is about 120 days, a glycated hemoglobin measurement will give a value which reflects an average glucose level for that period. Notably a meal high in glucose will not be reflected in a high glycated hemoglobin or serum albumin level. Thus, measurement of the glycated hemoglobin content gives a truer picture of the average circulating glucose levels and thus a truer picture of the long term condition of the patient. It's been reported that a 1% change in glycated Hb (% HbA1c) represents an average change of 300 mg/L in blood glucose levels over the preceding 120 days.
There are many literature and patent references that describe the measurement of A1C % utilizing antibodies to perform two separate measurements, one for the concentration of glycated hemoglobin the other for the concentration of total hemoglobin. The A1C % is calculated as a ratio of [Hemoglobin A1c]/[Hemoglobin]. Examples include U.S. Pat. Nos. 4,727,036, 4,247,533, 5,206,144, and 4,806,468. These patents describe the difficulty and imprecision of performing two separate assays for two different analytes and then calculating the A1C % as a ratio of [Hemoglobin A1c]/[Hemoglobin]. Using this method, the effect of measurement error is amplified, thereby increasing imprecision in reported A1C %.
Additionally, U.S. Pat. No. 5,407,759 and 6,162,645 imply that their methods are based on a single measurement A1C % detection. These methods, however, either use the term “single measurement” in a confusing manner, or do not describe an approach that can be applied universally for accurate measurement of clinical samples. In particular, neither the claims nor the detailed description within these patents clearly present how their “single measurement” approach can be accurately applied when the concentration of total hemoglobin varies significantly between samples. The physiological range of hemoglobin concentration ranges from 5 g/dL to 20 g/dL, a four-fold difference.